O2 Sensor Voltage Detector

[BretCahill]

I have an old carburetor aspirated engine with an O2 sensor. In the fuel
efficient mode, the O2 sensor dithers around 0.4 volts with the computer
opening and closing a solenoid valve every second or so. I can splice in a 50
K ohms/volt dc voltmeter and immediately see when I'm getting good gas mileage
but I don't like a voltmeter on my front seat and I want to install a small LED
indicator light instead. When the LED was flashing I'ld know I was saving gas.

An O2 sensor puts out too little current to power anything by itself. Is there
any way to wire up a 741 op amp + battery or other cheap circuit to power an
LED when the voltage goes above 0.4?

I'm guessing I'll need an amp gain of about 1000 and a voltage gain of 5.


Bret Cahill

 

[Mjolinor]

I have an old carburetor aspirated engine with an O2 sensor. In the fuel
efficient mode, the O2 sensor dithers around 0.4 volts with the computer
opening and closing a solenoid valve every second or so. I can splice in
a 50
K ohms/volt dc voltmeter and immediately see when I'm getting good gas
mileage
but I don't like a voltmeter on my front seat and I want to install a
small LED
indicator light instead. When the LED was flashing I'ld know I was saving
gas.

An O2 sensor puts out too little current to power anything by itself. Is
there
any way to wire up a 741 op amp + battery or other cheap circuit to power
an
LED when the voltage goes above 0.4?

I'm guessing I'll need an amp gain of about 1000 and a voltage gain of 5.

I did more or less this as part of the LPG control system on my Merc. I took
the O2 (lambda) sensor and fed it directly (bigish resistor to limit
current) into the AtoD of a 622 PIC and had about 7 LEDs on it, yellow in
the middle, red = rich and green = lean. It worked fine with very few
external components. There was one major problem in that the PIC wouldn't
work off the voltage I needed (very close to supply minimum), it failed to
boot correctly so I added a bit of code that switched a resistor in the
voltage supply regulator to drop the supply voltage once the PIC had booted
so that Vref was low enough for the lambda sensor with no amplification
needed.

 

[Terry]

BretCahill threw some tea leaves on the floor
and this is what they wrote:

An O2 sensor puts out too little current to power anything by itself. Is there
any way to wire up a 741 op amp + battery or other cheap circuit to power an
LED when the voltage goes above 0.4?

I'm guessing I'll need an amp gain of about 1000 and a voltage gain of 5.

The O2 sensor also will be damaged if you draw more than a few
microamps from it. Make sure that the load resistance is in the
meghoms.

--
Kind Regards from Terry
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